1. Field of the Invention
The present invention relates to an electric motor which extends an output shaft from a revolution unit provided outside of an engine case to inside the engine case, and a manufacturing method of the electric motor.
2. Description of the Related Art
For example, in a mechanism which changes a valve lift amount of an intake valve provided to each cylinder of a multicylinder engine, it is known to use an electric motor as a driving source of the mechanism, as is shown in Japanese Patent Laid-Open No. 2004-270608 (FIG. 1).
This type of the electric motor is equipped with a bracket fixed to a yoke accommodating a rotor and a commutator, and is fixed to the engine case via the bracket. To the bracket, a bearing which supports the output shaft of the rotor so as to be able to rotate freely, and a brush which contacts the commutator, are supported. To the engine case, a plurality of intake valves and an engine operating unit such as a cam shaft equipped with a cam which presses each valve lifter, and the output shaft of the rotor penetrates the bracket and extends into the inside of the engine case accommodating the engine operating unit.
Specifically, as is shown in Japanese Patent Laid-Open No. 2003-199282 (FIG. 2), such electric motor is equipped with, as a configuration for supplying electricity to a winding wire of the rotor, a commutator provided to an outer periphery of the output shaft, a pair of brushes pressed against the commutator by a spring, a pair of brush holders which slidably supports each brush, and a pigtail wire electrically connected to the brush.
However, in the manufacturing process of such electric motor, upon assembling the bracket equipped with the brush holder and the brush, and the rotor equipped with the commutator, so as to make the brush abut against the commutator, it is necessary to make the brush move away from the commutator side against the biasing force of the spring, by pulling the pigtail wire temporarily, and to insert the commutator between a pair of the brushes. Therefore, there is a fear that the pigtail wire receiving load may disconnect or break, or the connecting portion between the pigtail wire and the brush may disconnect, and the like.
On the other hand, if the pulling force of the pigtail wire is small, there is a fear that when inserting the commutator between the brushes, the brushes may spring to the commutator side by the biasing force of the spring, so that the brushes and the commutator contacts and breaks the commutator.